The present invention relates to hot water systems, and more particularly to hot water systems of a so-called "recirculating" type intended to provide "instant" hot water throughout a building, i.e., providing water at a high temperature at the service outlets substantially instantly as the water emerges from any service outlet, regardless of how far the particular service outlet is from the water heater, and regardless of the tendency of the hot water service line to be cooled by the cooler temperature of the ambient air through which the service line passes.
The hot water system as herein involved is commonly referred to as a "domestic system", i.e., a system which provides hot water for use as such, such as for washing, etc., in contrast to heating purposes; and it is called "domestic" in that sense, even though it is likely more for commercial buildings than for private residences.
Hot water systems of recirculating type are most frequently used in buildings of large size or in which the length of pipe used for hot water supply creates an undesirable length of time for delivery of hot water from where it is stored to the various service outlets throughout the building.
Such a system consists of a hot water supply pipe, from which hot water is supplied from the hot water tank to the service outlets, and a return pipe, which connects the last point of the supply pipe back to the hot water tank, creating a continuous loop of pipe through which water unused from any service outlet may flow back to the storage tank. There is often included a recirculating pump, in the return pipe, to promote flow in the desired direction toward the tank; and a check valve is installed in the return pipe, usually somewhere near the pump, to stop the water from flowing in an undesired direction.
The pump of such a system is operated to circulate the hot water from the storage tank through the supply pipe, and back to the storage tank via the return pipe; and the result is that the supply pipe is kept constantly at maximum operating temperature providing instantaneous hot water to the service outlets along the supply pipe.
Such systems of the prior art desirably nearly eliminate the time required for delivery of hot water from the hot water storage tank to the service outlets, and greatly reduce the amount and the heat content of water wasted by the user running water from the hot water service outlets until the water becomes usably hot, as would be the situation in a system where there is no circulation to keep water hot at all service outlets.
However, a disadvantage of recirculating hot water systems of the prior art is a substantial waste of energy in the form of heat loss from the water throughout the system during circulation. The circulated water that returns to the storage tank must be accordingly reheated back to the desired operating temperature. This condition constantly exists as long as the water is circulated, usually 24 hours a day.
Another disadvantage of prior art systems of continuous circulation is that in warm weather operation; for as the circulated water is losing heat into the building, the air conditioner load of the building correspondingly increases so as to remove from the building the heat dissipated into it by the hot water circulating system. This condition is not fully offset by a converse advantage during winter months, because of a lack of efficiency for heat transfer usefully into the building; i.e., that dissipated heat from the circulating hot water loop is usually located in floors, walls, or other areaways which do not achieve efficient heating of the building.
Another system available in the prior art is a system that incorporates a heat sensing thermostat that will disable the circulating pump when the temperature of the water at the thermostat reaches a desired level. The disadvantage of this system is that the heat-sensing thermostat is usually installed in the return pipe, very near the circulation pump, which itself is installed at the downstream end of the return pipe near the hot water tank.
In this prior art arrangement or configuration, the entire system is being regulated by the temperature which exists at the end of the return pipe; and this results in the entire circulation loop still being maintained at a fairly high temperature level, but this is wasteful of energy due to the keeping of the return line hot even though the return line is a long portion of the overall circulation loop, and the temperature of the return line water is of no significance to the temperature of the water in the supply pipe portion which contains the service outlets.
The above disadvantage could theoretically be minimized by installing the thermostat at the end of the supply pipe; however, that location is usually so remote and far away from the circulating pump, that the factors of installation of wiring of that tremendous length, together with the usual relative inaccessibility of that remote location, having meant that such an installation of the thermostat at that remote location seems not to have been considered as a practical solution.
Even an attempt to locate service outlets along the entire loop, to minimize the length of what would be just a short return line portion with no service outlets, is also not effective in this regard, because it would increase the overall length of pipe which would be required to be at the desired operating temperature of a service outlet use.
Thus in contrast to the prior art recirculating systems, the present inventive concepts provide a controlled recirculating domestic hot water system which has the advantages of nearly instantaneous hot water availability at all service outlets, yet which is more conservative of energy consumption than are previous recirculating hot water systems.
An additional achievement of the present invention is the provision of a recirculating hot water system control which is easy to install, is adjustable by the user to meet various installation conditions, and which is fully automatic in its operation.